Refrigeration compressor oil testing process and apparatus

ABSTRACT

A process and apparatus for determining the amount of contamination in the lubricant phase of a refrigeration system. The process utilizes a clear glass tube which contains an inert substance such as glass beads coated with a solvatochromic compound, preferably the solvatochromic compound is a mixture of Benzophenoxazine and Benzophenoxazone. A sample of the lubricant to be tested is passed into the glass tube and passes over the glass beads, picking up a portion of the solvatochromic compound. A white absorbent material such as sterile cellulose is positioned adjacent the coated substrate and the color reaction between the lubricant and the solvatochromic compound is clearly evident on the white absorbent material which then can be compared with a standard set of colors to determine the amount of the contamination.

THE FIELD OF THE INVENTION

The field of invention is refrigeration system servicing, and moreparticularly a detector tube assay employing a solvatochromic indicatorfor use in refrigeration system servicing.

BACKGROUND OF THE INVENTION

Refrigeration fluids are split into two phases, first the refrigerantphase, which is typically a low boiling point fluorocarbon gas, liquidor vapor, and secondly the oil phase, which can be either a mineral,alkylbenzene, polyol ester or polyalkylene glycol lubricant. Applicantis the inventor of a refrigerant gas contamination detector kit shown inU.S. Pat. No. 5,419,177. The specification of this '177 patent isincorporated by reference herein.

The '177 patent relates to detector tube analysis of contaminants in arefrigerant gas under pressure. The present invention specifies adetector tube for determining the level of contaminates that are presentin the oil phase.

In general, both phases will exhibit some degree of contamination in theform of water since it is nearly impossible to purify or render thefluids fully anhydrous. Although not desirable, water is alwaysincidental and inherently present. Water levels that exceed 10 ppm asmeasured in the refrigerant phase or water levels that exceed 50 ppm asmeasured in the oil phase can undergo hydrolysis to form detrimentalacids when subjected to the heat and compression of refrigerationequipment cycling. Typically a high moisture content will promoteinorganic acids to form out of the refrigerant and organic acids to formout of the lubricants over the working life of the refrigeration system.Neglect and the lack of preventative maintenance in the detection ofhigh moisture and acid formation are conditions that can lead topremature compressor or other associated refrigeration componentfailures.

Obtaining an oil sample for testing can be very labor intense. Forexample, the service technician must remove anywhere from 1 to 50milliliters of oil from a compressor crankcase of a sealed system. Sincemost all compressors of the hermetic variety have no oil tap or drainplug, the equipment must be taken off line and opened. This involves theremoval and recovery of the pressurized refrigerant gas in the system,removal and inversion of the compressor to pour out an oil sample fortesting; then reinstallation of the compressor, complete evacuation ofthe system and finally recharging with refrigerant gas for eventualequipment start-up and on-line duty.

Laboratory sample submission for quantitative acid and/or moistureanalysis is generally too impractical for the average service technicianversus the availability of an instant on-site test.

PRIOR ART

Traditionally, field test methods for determining the acid content ofthe oil phase of a refrigeration system is limited to pH indicators.Typically, the test kit contains a pH dye such as Bromophenol Blue orother pH indicating solutions or strips. The problems with the use of pHindicators in refrigeration diagnostics are bountiful, in that, (1) thepH range of indicator dyes are too broad, (2) a definitive end point(color change) may be masked or buffered by certain oil additives, (3)the oil type being tested may exhibit solubility problems with the testsolution or strip, (4) moisture levels are not indicated, and (5) pHdyes are more reliable with aqueous media than with organic solvents.

With the advent of solvatochromic chemistry, a more accurate andreliable field test for oil contamination is possible. However, thesolvatochromic dyes of the Pyridium-N-Phenol Betaines, described in U.S.Pat. Nos. 4,677,076, 4,677,079 and 4,722,983 failed due to their lack ofdistinct or discernable color differentiation in the visible range whensmall shifts in solution polarity must be quantified. ThePyridium-N-Phenol Betaines along with the classic solvatochromics of theIndoanilines, Carbonylpyridiums and Nitroanilines all require the use ofsensitive colorimetric instruments to measure differences in colorintensity.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a more definitiveoil phase test which will be easy to use in the field and provide betterquantitative results relative to the degree of contaminants therein. Theoil phase test is preferred but not limited to a detector tube assaybeing of the same construction and/or adaptability to the detector tubeholding device described in U.S. Pat. No. 5,419,177 which isincorporated herein by reference.

The specification for an indicator material shall be formulated with adye or dye combination of the solvatochromic Benzophenoxazine -Benzophenoxazone compounds.

This invention in particular relates to compounds and/or materials thatwill exhibit color transitions or separations when small shifts in thepolarity of a solvent must be determined. Specifically, but not limitedto, refrigeration compressor oil that becomes more polar due tomoisture, acid, dissolved metals or other aggressive polar adulterants.

DETAILED DESCRIPTION OF THE INVENTION

Solvatochromism is expected when the oil polarity has undergone change.Assume that a virgin anhydrous oil or nearly anhydrous oil representsthe ground state; then a more excited state can be induced by theaddition of adulterants such as water, acid, base and/or otheraggressive ionic materials.

A small group of dyes are known to undergo color transition with changesin solution polarity and these dyes may be tailored to act as a probe.Ideally, the probe will be sensitive enough to promote a definite,distinguishable color transition from the ground state, stepwise tohigher polar states. The color transitions specific for this inventionmust be readily identifiable in the visual range since the averageservice technician is not familiar with the application and use ofcolorimetric instrumentation.

The best suited solvatochromic dyes for this invention were determinedby exhaustive chemical screening. It was discovered that the best dyecandidates belong to the Benzophenoxazine and/or Benzophenoxazonefamilies having the basis structure: ##STR1##

When X is an amine, alkyl amine or dialkylamine group and R is an alkylamine or dialkylamine containing 1-10 carbon atoms, derivatives of theBenzophenoxazine family are represented. ##STR2##

When X is an oxygen and R is alkylamine or dialkylamine containing 1-10carbon atoms, derivatives of the Benzophenoxazone group are represented.

The Benzophenoxazines are typically prepared by reacting 5-diethylamino-2 nitrosophenol with 1-naphthylamine. The Benzophenoxazones areformed by refluxing the Benzophenoxazine with sulfuric acid.

The oxazine compounds can be treated with a hydroxide, chloride orsulfonated to form radical salts. ##STR3## y=1 when treated with aChloride or Hydroxide y=2 when Sulfonated

The radical salts offer similar degrees of solvatochromism, but canexhibit different degrees of solubility with the target solvents. A saltmust be chosen that will dissolve in the target solvent/solvents inorder for a solvatochromic effect to occur. A radical salt of theBenzophenoxazine can be tailored to exhibit more or less solubilitycharacteristics for the target solvent. The ratio of Benzophenoxazine toBenzophenoxazone may be adjusted to limit or broaden the solvatochromicproperty's range or effect.

Experimentally then, each oxazine and oxazone dye can be dissolved invarious organic oils or solvents. Coloration of the oil or solvent willvary based on the minute' differences in polarity. For example, apurified non-polar solvent represents a ground state and would exhibit alight coloration, while a more polar solvent representing a more excitedstate would exhibit a darker color.

In practice, the lubricants listed below are the most conventional andpredominate oils used in the refrigeration industry to date:

Mineral Oil (MO)

Alkylbenzene (AB)

Polyol Ester (POE)

Polyalkylene Glycol (PAG)

Virgin samples of the above oils were obtained and allowed to dry forone week over anhydrous silica gel, then passed through a columncontaining Brockman I activated alumina. The results from Karl Fischertitrations on the dried solvents indicated that the water content of theliquids did not exceed 5 ppm. The oils now represent a near groundstate. Alloquats from each oil were then adulterated with the additionof various amounts of water, acid and combinations of water and acidthat would typically be found in operating refrigeration compressors andthereby represent different excited states. It should be noted that theacidic component was a 50/50 mixture of hydrochloric and oleic acidswhich are the two most predominate acids of formation within arefrigeration system.

The solvatochromic oxazine and oxazone dyes of the radical hydroxideform were allowed to dissolve, in each near ground state oilrespectively, and the color change noted:

GROUND STATE OIL TEST

    ______________________________________                                        GROUND STATE OIL TEST                                                         With Oxazine    Oxazone    Oxazine + Oxazone                                  ______________________________________                                        MO      no color    pale yellow                                                                              bright yellow                                  AB      pale yellow yellow     yellow/brown                                   POE     yellow/orange                                                                             orange     orange                                         PAG     orange      orange     pink                                           ______________________________________                                    

The natural order of polarity of these solvents are ascending, beingthat MO is nonpolar, AB is slightly polar, POE is moderately polar andPAG is the most polar solvent. A definite solvatochromic shift isconfirmed with the dyes and dye combinations by the distinctive colortransition from no color to yellow to orange to a weak red (pinkish).

An extensive study was conducted to determine which individual dye ordye combination would give the best color resolution as well as adefinitive stepwise color transition with adulterated oils. All thetrial and error data revealed that a combination of oxazine and oxazonewere far superior for color differentiation when each isolated dye ordye derivative was tested.

The optimum dye mixture was mainly composed of the radical hydroxideoxazine with a counter balance of from 0.001 to 0.010% oxazone, whereabout 0.005% oxazone is preferred.

The test observations when 0.04 grams of the optimized solvatochromicdye is dissolved in 100 grams of the adulterated oils below.

CONTAMINATED OIL TEST

    __________________________________________________________________________    CONTAMINATED OIL TEST                                                                         25 ppm                                                                             40 ppm                                                                            50 ppm                                                                             90 ppm                                                                            150 ppm                                                     water                                                                              water                                                                             water                                                                              water                                                                             water                                       25 ppm 40 ppm                                                                             90 ppm                                                                            10 ppm                                                                             25 ppm                                                                            25 ppm                                                                             50 ppm                                                                            100 ppm                                     water  water                                                                              water                                                                             acid acid                                                                              acid acid                                                                              acid                                        __________________________________________________________________________    MO yel org  mag pink lav mag  vio blue                                        AB yel org  mag pink lav mag  vio blue                                        POE                                                                              org pink mag pink lav mag  vio blue                                        PAG                                                                              org pink mag pink lav mag  vlo blue                                        __________________________________________________________________________

It can be concluded that a nearly quantitative solvatochromic shift,yellow to orange to pink to lavender to magenta to violet to blue, isestablished. A subjective evaluation is forwarded being that a colorless than magenta being yellow, orange, pink or lavender would indicatethat an acceptable amount of water-acid contamination is present in thebulk lubricating oil, and any color intensity magenta or greater beingmagenta, violet or blue would indicate a highly polar and adversecondition within the bulk lubricant. The criteria for the pass/failscenario is in alliance with the standards set forth by therefrigeration industry, where the threshold limit for water should notexceed 50 ppm and the sum of acid plus water be less than 70 ppm intotality.

It should be noted that it is the amount of oxazone a component (about0.005%) added into the dominate oxazine dye formulation that balancesthe final color scheme. Addition of excess oxazone will cause greaterred shifts while insufficient or when no oxazone is incorporatedblue/violet shifts occur too prematurely with initially more polar POEand PAG solvents.

It is conceivable that an oil or solvent be charged with asolvatochromic dye or dye complex in order to monitor the condition ofthe oil or solvent over time. Such applications may be useful indetermining when to change the oil or solvent in air compressors, vacuumpumps or other internally lubricated mechanisms. Or, if it is notdesirable to charge the oil or solvent with dye, a small sample of oilcould be externally tested with a strip or solution containing the dye.

A detector tube construction for sampling oil directly from a sealedrefrigeration system is forwarded herein, since a detector tube assayoffers an instant evaluation of the oil phase without disassembly oroperating downtime.

Experimentally, 0.05 to 0.25% solution of the oxazine/oxazone dye wasdissolved in anhydrous methanol, with 0.10% being preferred. Thesolution was coated onto an inert substrate such as powderedborosilicate glass and the alcohol and any associated water wasevaporated off with heat in a dry box circulating dry nitrogen gas.

Into a 3.5" 1×5/32" diameter detector tube, a dry and sterile acrylicbating was compacted to a length of 1/2" assembled in the same dry box.About a 2" fill of the dye coated powdered glass was then packed abovethe acrylic batting. The detector tube ends were then sealed with rubberstoppers as to conform to the construction of a detector described underthe previous patent.

The sealed detector tube was removed from the box and inserted into adetector tube holding device (see U.S. Pat. No. 5,419,177, FIGS. 2-7,and columns 2-4) that was connected to the suction (return line) serviceport of an operating refrigeration system. It is known that smallamounts of oil will be carried with the circulating refrigerant gas, andby connection to the service port, refrigerant gas and trace amounts ofoil will bleed through the detector tube. It should be noted that theamount of oil necessary to obtain a good test result could be as smallas 10 microliters. A de minimis bleed for about 15 seconds caused traceamounts of oil to enter into the detector tube, flushed through the dyesubstrate and deposited an orange stain onto -the acrylic batting. Thecontaminant level of the oil was known prior to the test to contain 35ppm water and less than 0.10 ppm acid. Thus, the result was consistentwith laboratory trials from a representative sample.

Subsequent testing on many other refrigeration systems also yieldedresults that consistently correlated with the lab data. Experimentally,the dye a was coated onto a variety of other different substrates inattempts to find the most suitable substrate. Any substrate that had apolar character performed less satisfactorily than those that werenon-polar or otherwise highly inert. Different fabric or stain enhancingmaterials were substituted for the acrylic batting. Sterile cellulose,cotton, wool and non-polar polymer fabrics worked satisfactorily withthe natural fabrics being preferred due to their more permanent colorfastness to a dye wash. Some ion exchange resins were also tested withsatisfactory results.

The specific detector tube arrangement therefore consists of asolvatochromic dye of the Benzophenoxazine and/or Benzophenoxazonegroups coated onto a substrate which is upflow from a stainable media,developer or indicating layer. Oil is allowed to enter the tube, come incontact with and wash through the dye segment and then stain a secondsegment. The resultant color which is retained by the second segmentindicates the polarity of the oil being sampled. The endpoint color canthen be visually matched to a color chart for a semi-quantitativeanalysis.

The present embodiments of this invention are thus to be considered inall respects as illustrative and not restrictive; the scope of theinvention being indicated by the appended claims rather than by theforegoing description. All changes which come within the meaning andrange of equivalency of the claims are intended to be embraced therein.

I claim:
 1. A color sensitive process for determining the amount ofcontamination in a lubricant sample comprising:passing a lubricantsample over a carrier containing a color sensitive chemical, said colorsensitive chemical being reactive with said lubricant depending upon thedegree of contamination of said lubricant to provide a colored reactantsolution; conveying the colored reactant solution into an inert, whitecarrier held within a clear tube; observing the resulting coloredreactant on said inert white carrier; and comparing the color with acolor standard to determine the amount of contamination in saidlubricant sample.
 2. The color sensitive process of claim 1 wherein saidcarrier is selected from the group consisting of glass beads, paper,polymer, and resin gels.
 3. The color sensitive process of claim 1wherein said inert white carrier is selected from the group consistingof acrylic batting, sterile cellulose, wool, resin, paper, polymers andgels.
 4. A process for determining the amount of contamination of alubricant sample comprising the steps of:coating an inert substrate witha solvatochromic dye selected from the group consisting ofBenzophenoxazine and Benzophenoxazone to produce a coated substrate;positioning the coated substrate within the interior of a clear tubehaving an entrance end and an exit end; placing a white absorbentmaterial adjacent said coated substrate and between said coatedsubstrate and said exit end; introducing a sample of the lubricant intothe entrance end of said clear tube; passing a gaseous carrier streaminto the entrance end to move the sample of lubricant through saidcoated substrate and into said white absorbent material to produce acolored substrate portion; and viewing the resulting color of thecolored substrate portion which provides a measure of the contaminationof the lubricant sample.
 5. The process of claim 4 wherein said inertsubstrate is selected from the group consisting of glass beads, polymer,resin, paper fiber and gel.
 6. The process of claim 4 wherein said whiteabsorbent material is selected from the group consisting of acrylicbatting, sterile cellulose, cotton and wool.
 7. A article useful fordetermining the amount of contamination in a sample of lubricant takenfrom an air conditioning system, said tube comprising:a clear, hollowelongated member having an entrance end and an exit end; an inertcarrier material coated with a solvatochromic chemical held within saidclear, hollow elongated member near the entrance end thereof; and awhite absorbent material held within said clear, hollow elongated memberadjacent said inert carrier material and positioned between said inertcarrier material and the exit end of said clear, hollow elongatedmember.
 8. The article of claim 7 wherein said inert carrier material isglass beads.
 9. The article of claim 7 wherein said solvatochromicchemical is selected from the group consisting of Benzophenoxazine andBenzophenoxazone.
 10. The article of claim 7 wherein said whiteabsorbent material is selected from the group consisting of acrylicbatting, sterile cellulose, cotton, wool, polymer, gel, paper, resin orthe like.